Background Art No. 1 (Amorphous Transparent Electroconductive Film, Sputtering Target of Starting Material Thereof, and Amorphous Transparent Electrode Substrate)
A TFT-LCD, an STN-LCD, and a TN-LCD are used in a scope from relatively small-sized display sections of a cellular phone, a personal digital assistant (PDA), a notebook-sized personal computer and so on to large-sized display devices such as a monitor of a computer and a television screen.
In recent years, materials for electrodes of TFT-LCDs are shifting from amorphous silicon (referred to as amorphous Si hereinafter) type materials to polysilicon (referred to as “poly Si” hereinafter) type materials. The aim of this shift is to apply the LCDs to display sections for cellular phones coping with moving images or television screens by making the switching speed thereof large.
In the case of conventional amorphous Si type materials, the mobility thereof is about 1 cm2/V·sec.; therefore, an improvement in the switching speed is restricted. Thus, an attempt is made wherein amorphous Si is crystallized by a given method to prepare poly Si and the mobility thereof is improved to make the switching speed high. It is known that the mobility of this polycrystal Si (poly Si) type electrode material is improved up to about 200 cm2/V·sec.
It is reported that: in continuous grain boundary poly Si, crystal grains thereof are large and boundary lines between the crystals are continuous; accordingly, the mobility thereof is 400 cm2/V·sec. or more. In this way, about continuous grain boundary poly Si, researches for using the Si in pseudo monocrystal silicon TFT technique are widely made (see, for example, Non-patent Document 1, which will be listed up later).
Meanwhile, as electrodes of liquid crystal display devices using a liquid crystal, such as TFT-LCDs, there are used transparent electrodes which are transparent and have electroconductivity for transmitting electric signals to the liquid crystal.
As one of the transparent electrodes, indium thin oxide (ITO), which is made of indium oxide-tin oxide having transparency and a small resistivity, is known and is widely used. This ITO is a material having a small resistivity (resistivity: 200 μ·Ω·cm, carrier density: 1.0×1021/cm3, and mobility: 40 cm2/V·sec.), but has drawbacks such that a strong acid should be used when the ITO is etched. It is also known that if the carrier concentration in ITO is increased, the mobility thereof generally falls by ion scattering.
In order to solve such problems, Patent Documents 1 and 2, which will be listed up later, disclose a material comprising indium oxide-zinc oxide and further comprising Sn, Ga or Ge. It is known that a weak acid can be used to etch this material and the material is excellent in workability. However, the resistivity of the material disclosed in Patent Documents 1 and 2 is not very low. The mobility of the material is about 20 cm2/V·sec., which is a lower value than that of poly Si.
Patent Document 3, which will be listed up later, discloses a technique of making a material made of indium oxide-zinc oxide into a film by a low-voltage sputtering method in order to make the resistivity of this material low. However, in order to sputter the material at a low voltage, it is unavoidable to make the magnetic field of the sputtering device strong and overlap AC plasma with DC plasma. Thus, there arise problems that the device is expensive and further operations or steps therefor are complicated.
Patent Document 4, which will be listed up later, discloses a transparent electroconductive laminate wherein a transparent electroconductive film made mainly of indium, tin, zinc and oxygen atoms is formed on a polymer substrate and the composition at% satisfies the following: Zn/(In+Zn)=0.01 to 0.1 at %, Sn/(In+Sn)=0.01 to 0.1 at % and further Zn/(Zn+Sn)=0.55 to 1 at %. However, the resistivity of such a laminate is 250 μ·Ω·cm or more. It cannot be said that this resistivity is far lower than conventional resistivities. When the transparent electroconductive laminate having the above-mentioned composition is heated, the laminate is crystallized. Thus, residues may be generated when the heated laminate is etched.
Meanwhile, Patent Documents 5 and 6, which will be listed up later, disclose sputtering targets obtained by adding, to indium oxide-zinc oxide, tin oxide in an amount of 20 to 2000 ppm. The main aim of the Patent Documents 5 and 6 is to control the crystal structure of the sputtering target and improve the mechanical strength thereof. Thus, no heed is given to the matter that the sputtering target is used to produce a film having a relatively low resistivity. Therefore, it appears that a low resistivity cannot be realized.
Patent Document 7, which will be listed up later, discloses a production of a material which is made of indium oxide-zinc oxide and is low in resistivity by controlling the crystal structure of a sputtering target used for producing this material.
Patent Document 8, which will be listed up later, discloses a process of producing a transparent electroconductive film low in resistivity by adding Re, Os, Mo or W to indium oxide or ITO and then controlling the orientation of the crystal thereof.
Patent Document 9, which will be listed up later, discloses a sintered, electroconductive metal oxide which is low in resistivity and is produced by adding, to indium oxide, Nb or Hf in an amount of 1 to 20% by weight thereof. Patent Documents 10 to 13, which will be listed up later, disclose transparent electrodes wherein Zr is added to indium oxide. However, all methods described in Patent Documents 7 to 13 have a problem that the resultant transparent electrodes have crystallinity and thus residues are generated by etching or nodules are generated at the time of sputtering.
Non-patent Document 1: “Electronic Material”, Kogyo Chosakai Publishing Inc., December, 2002, p.26
Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 6-234565
Patent Document 2: JP-A No. 7-235129
Patent Document 3: JP-A No. 9-71860
Patent Document 4: JP-A No. 2001-126538
Patent Document 5: JP-A No. 2001-131736
Patent Document 6: JP-A No. 11-128122
Patent Document 7: Japanese Patent Application National Publication No. 2001-539936
Patent Document 8: JP-A No. 7-278791
Patent Document 9: JP-A No. 3-15107
Patent Document 10: JP-A No. 6-160876
Patent Document 11: JP-A No. 7-218924
Patent Document 12: JP-A No. 2002-226966
Patent Document 13: JP-A No. 2002-373527
Background Art No. 2 (Color Filter for Liquid Crystal Display)
In color liquid crystal displays, color display is attained by use of optical property of liquid crystal, optical members, an external light source or the like. One of the optical members for attaining color display is a color filter. This color filter 100 for liquid crystal display generally has:
(1) an electrically insulating transparent substrate 10 which is also used as a substrate for forming a liquid crystal panel,
(2) plural colored layers 12 arranged on this electrically insulating transparent substrate 10 so as to have a given pattern, and
(3) a transparent electrode 14, for driving liquid crystal, which is formed on these colored layers 12. This situation is shown in FIG. 2A. In the present patent, this is called type 2A. The colored layers 12 are composed of a red colored layer 12R, a green colored layer 12G, and a blue colored layer 12B. FIG. 3 is a schematic structural view illustrating only the basic structure of the color filter 100 for liquid crystal display. Actually, a protective layer is formed between the colored layers 12 and the transparent electrode 14 in many cases. As will be detailed later, light-shielding layers are formed between the respective colored layers 12R, 12G and 12B in many cases. In FIGS. 2A and 2B, these light-shielding layers and soon are omitted not to be illustrated.
The position of the colored layers 12 and that of the transparent electrode 14 maybe reverse. In this case, the color filter 100 for liquid crystal display has, as its basic structure, the following:
(4) an electrically insulating transparent substrate 10 which is also used as a substrate for forming a liquid crystal panel,
(5) a transparent electrode 14, for driving liquid crystal, which is formed on this electrically insulating substrate 10, and
(6) plural colored layers 12 arranged on this transparent electrode so as to have a given pattern. This situation is shown in FIG. 2B. In the present patent, this is called type 2B.
The colored layers 12 are each a layer which selectively transmits a ray having a specific wavelength out of rays emitted from a light source, and are plural colored layers 12 having different spectral transmittance characteristics in accordance with whether multicolor display is performed or full color display is performed. For example, when full color display is performed by additive color mixture, layers of the following three kinds are used: a red colored layer 12R having a high spectral transmittance in a red wavelength range; a green colored layer 12G having a high spectral transmittance in a green wavelength range; and a blue colored layer 12B having a high spectral transmittance in a blue wavelength range.
As the arrangement pattern of these kinds of colored layers 12, a stripe type, a mosaic type, a triangle type, a 4-pixel arranged type, and so on have been hitherto known. Appropriate one out of these patterns is used in accordance with the operation mode of the color liquid crystal display or the performance thereof.
In many cases, a light-shielding layer is formed between a colored layer and another colored layer, or on a transparent protective layer which will be detailed later. This is for preventing a fall in the contrast or color purity based on leak light. The light-shielding layer in this case is made of metal chromium, a colored photoresist or the like. This light-shielding layer is arranged so as to be positioned between pixels when the front plane of a color liquid crystal display equipped with the color filter is viewed. The form of the whole thereof is generally a matrix form or stripe form in many cases.
As described above, the transparent electrode 14 for driving liquid crystal may be arranged between the electrically insulating substrate 10 and the above-mentioned colored layers 12 (type 2B). In many cases, however, the electrode would be arranged, directly or indirectly across a transparent protective layer, over the colored layers 12 in order to prevent an increase in the threshold voltage of the liquid crystal display element or a decline in the sharpness of the rise thereof.
The shape of this transparent electrode 14 for driving liquid crystal is varied in accordance with the operation mode or the performance of the color liquid crystal display, or other factors. The electrode 14 is formed into plural stripes or a single film. In FIGS. 2A and 2B, a situation that the whole of a screen is formed into a film, or into the so-called “solid” form is illustrated. In the case of an active matrix type TFT liquid crystal display device, this transparent electrode in the “single film” form has been hitherto arranged on the side of its color filter in many cases.
The transparent protective layer is formed in order to improve the flatness or the smoothness of the transparent electrode and protect the colored layers. As this liquid-crystal-driving transparent electrode, an indium thin oxide (ITO) film has been hitherto used in many cases. This is because the ITO film is good in transparency and electroconductivity and can be sufficiently etched with a strong acid.
Incidentally, the following lists up documents about the prior art related to the invention of the present patent application.
Patent Document 14: JP-A No. 11-352483
Patent Document 15: JP-A No. 2002-202511
Patent Document 16: JP-A No. 2003-143525
Patent Document 17: JP-A No. 07-120612
Patent Document 18: JP-A No. 09-101408
Patent Document 19: JP-A No. 09-005514